RU2498014C2 - Method to determine frost heave of soil during freezing of seasonally thawing layer - Google Patents

Abstract

FIELD: construction.

SUBSTANCE: method to determine frost heave of soil during freezing of a seasonally thawing layer includes drilling of a well before start of its thawing, sampling of soil, measurement of depth of seasonal thawing ξ, definition of dry soil density in samples ρ_d,th. In addition wells are drilled after freezing of the seasonally thawing layer, on the samples they additionally define density of dry soil after freezing of the seasonally thawing layer ρ_d,f, and the heave value is determined in accordance with the given dependence.

EFFECT: reduced labour intensiveness of works, increased accuracy of determination of heaving value, provision of material intensity reduction.

Description

The invention relates to construction production and is intended to determine the frost heaving of the soil during freezing seasonally spreading layer.

There is a method of determining soil heaving, including drilling a well, installing a benchmark in it to a depth exceeding the depth of seasonal thawing of the soil, filling the sinus between the benchmark and the walls of the well with moist soil, installing the mark on the ground, observing the vertical movements of the mark relative to the benchmark for the entire period freezing of the soil layer [1].

The disadvantages of this method is the complexity due to equipment benchmarks, grades and long-term observations of heaving of the soil, as well as significant metal costs for the manufacture of benchmarks.

The closest technical solution is a method for determining frost heaving of soil during freezing of a seasonally spreading layer, which includes drilling a well before freezing, taking soil samples, measuring the depth of seasonal thawing ξ, determining the density of dry soil ρ _d , the density of mineral particles ρ _s , and soil moisture on the samples w, humidity over unfrozen water w _w (T _fh ), moisture yield strength w _L and rolling w _p , minimum temperature of the freezing zone T _fh , design temperature at the surface nt equal to the average temperature of the cooling medium during the freezing period and the calculation of the heaving according to the formula [2]

where ξ is the thickness of the soil layer before freezing; ρ _d is the density of the skeleton of the soil, g / cm ³ ; ρ _w is the density of water, g / cm ³ ; w is the moisture content of thawed soil; w _w (T _fh ) - content (by weight) of unfrozen water in frozen soil at a temperature of 0.57 T _fh ; T _fh is the minimum temperature of the freezing zone at which heaving stops; ζ = 0 for w≤w _u.fh and ζ = 0.09 for w> w _u.fh ; w _p - humidity rolling limit; T _0f is the calculated temperature at the soil surface, equal to the average temperature of the cooling medium during the freezing period.

The remaining parameters in formula (1) are determined by the corresponding dependencies and graphs.

The parameter K _b , expressing the ratio of moisture conductivity of thawed and frozen soils, in practical calculations can be taken equal

where w _sat is the full moisture capacity of thawed soil.

Parameter ψ is determined from the graphs in Figure 1 by the relations T _fh / T _0f for: a) sandy loam, b) loam, c) clay.

The correlation parameter η _s , which expresses the relationship between temperature and the content of unfrozen water in the freezing (heaving) zone, and temperature T _{fh are} determined from Table 1.

The first initial condition of heaving by humidity is determined by the dependence

where 0.92 is the density of ice, g / cm ³ .

Table 1 The values of the parameters η _c , k _w (T) and the heaving termination temperature Type of soil The number of soil plasticity, fractions of units The temperature of the cessation of heaving, T _fh , ° C The value of the parameter η _s Sandy loam 0.02 <I _p ≤0.07 -1.5 3,55 Sandy loam -2.0 5.00 Loam 0.07 <I _p ≤0.13 -2.0 4.25 Dusty loam -2.5 5.00 Loam 0.13 <I _p ≤0.17 -2.5 3.80 Dusty loam -3.0 5.35 Clay I _p > 0.017 -4.0 2,50

The critical value of humidity, which determines the second initial condition of heaving, is found by the formula

or

where w _L - soil moisture at the upper limit of ductility (yield strength); I _p = w _L -w _p is the plasticity number.

The value of w _cr at ρ _s = 2.7 g / cm ³ can be determined from the graph in FIG. 2 (dependence on humidity w _cr at the yield strength w _L and plasticity number I _p ).

The disadvantage of this method is the high complexity of the work to determine a large number of characteristics of physical properties and thermal state of the soil.

The purpose of the invention is to reduce the complexity of the work, improving the accuracy of determining the amount of heaving, which can reduce unnecessary costs in the construction of structures.

The goal is achieved by the fact that according to the method for determining frost heaving of the soil during freezing of the seasonally spreading layer, including drilling wells with sampling before and after freezing of the seasonally thawed layer, the depth of seasonal thawing ξ is measured, the density of dry soil before freezing of the seasonally thawed layer ρ _{d, th} and after it is frozen freezing ρ _{d, f} and calculate the swelling according to the formula

The heaving value is the product of the thickness of the soil layer before freezing ξ by the ratio of the increment of the thickness of the soil layer during freezing h _f -ξ and the thickness of the layer of thawed soil ξ

Let us express in formula (7) h _f and ξ through the corresponding soil volumes in the thaw V _th and frozen V _f states and an arbitrary soil cross-sectional area s

Depending (8) the volume of soil in thawed V _th, V _f and frozen states expressed in terms of dry weight of soil m _d and density ρ _{d, th} and ρ _{d, f}

Substituting (8) and (9) into (7), we obtain the calculated formula for frost heaving of freezing soil (6):

An example implementation of a method for determining frost heaving of soil during freezing of a seasonally spreading layer

The method was tested at the hospital "Tuymaada" Institute of permafrost SB RAS.

Before the freezing of the soil layer melted over the summer in early October, a thickness of ξ = 1.65 m was determined with a special metal probe. Then, a well was drilled using the core method to the entire depth of the thawed layer. Every 30 cm of the core, thawed soil samples were taken into cutting rings with a known volume (V _th ), packaged in accordance with the requirements of GOST 5180-2000, delivered to a soil laboratory, dried at a temperature of 105 ° C in an oven, and dried samples were weighed ( m _{d, th} ) and the density of the skeleton of thawed soil was calculated by the formula ρ _{d, th} = m _{d, th} / V _th .

The results of determining the volume of samples, the mass of dried soil and the calculation of the density of the skeleton of thawed soil are presented in the table below.

table 2 Sampling Depth h, m The mass of the dried soil sample m _{d, th} , g The volume of the cutting ring (wet soil) V _th , cm ³ The density of dry (skeleton) soil ρ _{d, th} , g / cm ³ 0.3 69.73 50.24 1,388 0.6 71.66 50.24 1,426 0.9 74.81 5,0,24 1,489 1,2 69.42 50.24 1,382

After freezing a layer of soil that melted over the summer in April, a well was again drilled 1 m from the first well to the same depth. Also, every 30 cm of the core, samples of frozen soil were taken to determine the density and moisture of the soil, packed, delivered to a laboratory with a negative temperature.

Samples for determining soil moisture were weighed (m _{f, 1} ), dried in an oven, dried samples were again weighed (m _{d, f} ), and frozen soil moisture was calculated using the formula w _f = (m _{f, 1} -m _{d, f} ) / m _{d, f} .

The results of weighing samples and determining soil moisture are given in the table below.

Table 3 Depth of selection
samples h, m Sample weight
m _{f, 1} , g Mass of dried
sample m _{d, f} , g Humidity of a frozen soil sample w
D.E. w _f = (m _{f, 1} -m _{d, f} ) / m _{d, f} 0.3 71.6 49.14 0.457 0.6 63,2 46.61 0.356 0.9 84.7 62.79 0.349 1,2 75.6 56.84 0.33

Samples for determining the density of the soil in accordance with GOST 5184-2000 were processed to a round shape, weighed in air (m _{f, 2} ), tied with a thin thread, dipped in kerosene and weighed in kerosene (m _{f, k} ) and the frozen density of the soil was calculated by the formula ρ _f = ρ _k m _{f, 2} / (m _{f, 2} -m _{f, k} ), then we found the density of the skeleton of frozen soil by the formula ρ _{d, f} = ρ _f / (1 + w _f ).

The results of weighing samples of frozen soil in air and kerosene with a density of p _k = 0.86 g / cm ³ and calculations of the density of frozen soil and the density of the skeleton of frozen soil are given in the table below.

Table 4 Sampling Depth h, m The mass of the sample in air m _{f, 2} , g The result of weighing samples in kerosene m _{f, K} , g The density of frozen soil p _f , g / cm ³ The density of the skeleton of frozen soil p _{d, f} , g / cm ³ 0.3 135.8 67.90 1.72 1.18 0.6 120,4 58.83 1.76 1.30 0.9 127.6 61.31 1.79 1.33 1,2 129.1 61.68 1.8 1.35

To compare the results of determining frost heaving of the soil by the proposed method at depths of 0.3; 0.6; Grades 0.9 and 1.2 m were laid, the vertical displacements of which were determined by leveling with respect to the stationary benchmark - a metal pipe embedded in the thickness of frozen soils to a depth of 9.0 m.

The calculated data and the results of determining heaving by the proposed method according to the formula h _fh = ξ (ρ _{d, th} / ρ _{d, f} -1) and leveling are shown in the table below.

Table 5 Depth Interval, m Power of the ith soil layer ξ _i , m Density
skeleton thawed
soil P _d.th , g / cm ³ Density
frozen skeleton
soil p _{d, f} , g / cm ³ The amount of heaving, cm by the proposed method on leveling

i-th layer

total

0.3-0.6 0.3 1.41 1.25 3.84 8.79 7.4 0.6-0.9 0.3 1.46 1.33 2.94 4.95 4.3 0.9-1.2 0.3 1.44 1.35 2.01 2.01 3.2

The maximum error in determining the heaving value of the proposed method is 18.8%, which is permissible under conditions of changing the density of the skeleton of the soil in the horizontal plane.

Industrial applicability. The invention can be successfully applied to determine the heaving of soils on the lines of linear structures when calculating the depth of the piers in frozen ground.

Information sources

1. Orlov V.O., Yolgin B. B., Zheleznyak I.I. Frosty heap of soils in the calculation of the foundations of structures. - Novosibirsk: Publishing House of Science, 1987. - 136 p.

2. The basics of geocryology. Part 5. Engineering geocryology. // ed. E.D. Ershov. - M.: Publishing House of Moscow State University, 1999 .-- 526 p.

Claims (1)

A method for determining frost heaving of soil during freezing of a seasonally spreading layer, including drilling a well before freezing, taking soil samples, measuring the depth of seasonal thawing ξ, determining the density of dry soil ρ _{d, th} on the samples, characterized in that the wells are additionally drilled after freezing of the seasonally spreading layer, the samples additionally determine the density of dry soil after freezing seasonally spreading layer ρ _{d, f} , and the heaving value is determined by the formula:

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